An emulsion is a dispersed system consisting of two immiscible liquids, in which small droplets of one liquid is dispersed in a second liquid. Emulsions with a droplet size in the range of less than 1 μm are often referred to in the literature as miniemulsions, nano-emulsions, microemulsions, etc. These “miniemulsions” are formed by dispersion or high-energy emulsion methods such as high-shear stirring, high-pressure homogenisers and ultrasound generators.
Miniemulsions are of great interest as pharmaceutical and cosmetic formulations. In the pharmaceutical industry a major problem is the efficient and efficacious delivery of drugs. It is well known that many promising drugs never make it to a final product because of difficulties in delivery. The problems with drug delivery tend to be related to the physical or chemical properties of the drug, administrative matters, such as approval for use, excipients, and engineering issues. Some of the major challenges of drug delivery are poor solubility, short in vitro (shelf-life) and in vivo (half-life) stability, low bioavailability, unacceptable side effects (due to systemic delivery) and regulatory issues.
A drug delivery system or formulation should have the following characteristics: ease of production, applicability to as many drugs as possible, physical stability, excipients that are well tolerated and accepted by regulatory authorities and available for large scale production allowable by regulatory authorities. Miniemulsions have properties that make them ideal for use in drug delivery including thermodynamic stability (long shelf-life), ease of formation, high surface area (high solubilisation capacity) and very small droplet size.
However, there are problems associated with the available miniemulsion formulations. High levels of non-active compounds are a hazard in cosmetics and drug delivery systems and many miniemulsions have high surfactant concentrations and in most cases have a high alcohol, solvent and co-solvent content in order to maintain stability. Further, many miniemulsions are created using high-energy processes, such as high pressures and high temperatures. For example, high temperatures are used to induce stability, which makes commercial production expensive. Additionally, miniemulsions created using processes such as ultrasonic emulsification, which are only useful for creating small batches, means reproducibility of the emulsion during commercial scale up is difficult.
Accordingly, the methods that are currently available for making miniemulsions that are feasible for formulating product are constrained. As such, there is a need for improved methods and formulations for miniemulsions for use as delivery systems for bioactive agents.